In the current rotation, Javier Assad is the youngest pitcher. He turns 29 this month. Taillon is 34 and on an expiring deal, Shota is 32 and on an expiring deal, Boyd is 35 and on an expiring deal. Horton and Brown are young-ish, but probably won't be seen this year. Cabrera is 28 with 2 years left.
We have two current relievers under 30. They are both 29, and also bad. Of the injured relievers currently on the 40 man, Palencia is 26, Hodge is 25. The other 6 are at least 28.
If this is a rebuilding pitching staff, it would be a very bad version of one. What it is is a cheaply made pitching staff designed to be just good enough to be carried by the offense and defense, and then it was completely wrecked by injuries.